var log = console.log;
var user = {username: "zhangsan",
            age: 20,
            sex: "male"
        };
log("username: %s", user.username); //字符串
log("age: %d", user.age); //整数 age:20
log("sex: %j", user.sex); //对象的占位符 sex: "male"

log(`${user.username}`);//模板字符串，变量放在${}里